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Space weathering of silicates simulated by successive laser irradiation: In situ reflectance measurements of Fo 90 , Fo 99+ , and SiO 2
Author(s) -
Loeffler M. J.,
Dukes C. A.,
Christoffersen R.,
Baragiola R. A.
Publication year - 2016
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12581
Subject(s) - irradiation , olivine , space weathering , analytical chemistry (journal) , materials science , laser , x ray photoelectron spectroscopy , mineralogy , spectral line , optics , reflectivity , chemistry , nuclear magnetic resonance , physics , astronomy , chromatography , nuclear physics
Pulsed‐laser irradiation causes the visible‐near‐infrared spectral slope of olivine (Fo 90 and Fo 99+ ) and SiO 2 to increase (redden), while the olivine samples darken and the SiO 2 samples brighten slightly. XPS analysis shows that irradiation of Fo 90 produces metallic Fe. Analytical SEM and TEM measurements confirm that reddening in the Fo 90 olivine samples correlates with the production of “nanophase” metallic Fe (npFe 0 ) grains, 20–50 nm in size. The reddening observed in the SiO 2 sample is consistent with the formation of SiO or other SiO x species that absorb in the visible. The weak spectral brightening induced by laser irradiation of SiO 2 is consistent with a change in surface topography of the sample. The darkening observed in the olivine samples is likely caused by the formation of larger npFe 0 particles, such as the 100–400 nm diameter npFe 0 identified during our TEM analysis of Fo 90 samples. The Fo 90 reflectance spectra are qualitatively similar to those in previous experiments suggesting that in all cases formation of npFe 0 is causing the spectral alteration. Finally, we find that the accumulation of successive laser pulses cause continued sample darkening in the Vis‐ NIR , which suggests that repeated surface impacts are an efficient way to darken airless body surfaces.